Many types of gas plasma display devices are known which use electrodes formed with a conductor composition deposited on a support plate by a screening process or the like. Cathode glow electrodes and associated conductor runs are formed of such material.
After considerable early experimentation with conductor compositions for use as thick film cathode electrodes, the gas plasma display industry settled on compositions containing nickel as the primary conductive component because of nickel's desirable electrical characteristics and chemical stability. Such compositions, which are usually referred to as pastes or inks, have now been used for many years. In addition to nickel, these inks also contain a glass frit binder, a vehicle, and other constituents, and, when used, the ink is deposited on a soda-lime glass plate or on dielectric layers previously deposited on this plate, and the assembly is then fired. It has been customary to formulate the nickel conductor ink for firing in either air or nitrogen.
The use of compressed air for the furnace atmosphere is desirable because it is relatively low in cost. However, the reactive components required for air firing nickel ink formulations are relatively expensive and cause effects which adversely affect the properties of cathodes and associated conductor elements. Some of these problems can be overcome by using nitrogen firing nickel inks which do not contain these reactive components and firing in a nitrogen atmosphere.
It was recognized early on that the key to optimum performance of nickel inks, with respect to physical and electrical characteristics and processing, is primarily the glass binder system. Since soda-lime float glass is the preferred substrate for these displays, a binder system having a working temperature below 590.degree. C. is necessary to prevent substrate distortion during the conductor firing operation. A wide variety of binders have been tried, and it was found that the most satisfactory compromise was a lead glass. Thus, a binder comprised entirely or in part of a lead glass has been widely used for air or nitrogen firing nickel inks. However, the fundamental problem with a lead glass binder is the relative ease with which reduction to metallic lead can occur, thus degrading the bonds within the nickel conductor and between the nickel conductor and the glass support plate, as well as forming sites for preferential accumulation of mercury which is present in the gas filling of the panel. These defects degrade cathode performance, degrade mechanical properties, and limit the life of the display device.
The present invention provides a new nitrogen firing conductor ink which includes a lead-free glass binder, can be fired in nitrogen, and avoids problems discussed above.